This invention relates to hole openers, specifically to openers which are designed to enlarge the diameter of drilled holes.
Drillers commonly have drilled holes and thereafter enlarged the hole for the intended purposes with hole openers and reamers which are designed to enlarge the diameter of the pilot hole or original bore diameter. Most openers or reamers known to applicant are devices having the cutting surfaces mounted on support arms which are mounted on the opener body and having their radial axis directed inward to support the rotating cutter head. The abrasion and load experienced by such bodies wears the outer surfaces of the support arms as the opener moves through the formation to be opened and ultimately may cause the support arms to fail.
The normal operating problems of conventional hole openers or reamers is exacerbated when drilling horizontal or near horizontal applications. In such situations, the load and wear characteristics on the support arms may cause early and catastrophic failure of the arm structure and often results in loss of cutters in the borehole itself. Additionally, in horizontal or near horizontal applications, the support arms of conventional openers create additional torque on the tubular string which carries the hole opener body. These problems may cause failure of both the support arms and loss of cutters in the hole requiring expensive retrieval operations and delay the completion of the operation.
Other economical considerations warrant consideration. In conventional hole openers, the hole opener body is limited by its design to essentially one-size of diameter. The design of the conventional hole opener does not permit alternative sizes of holes to be made with the same body because the span of the support arms fits only one size of cutter. If alternative diameter holes are required, a whole new body must be acquired to open the hole. This requires additional trips into and out of the hole to change the opener and cutter body. Additionally, conventional hole openers are designed to operate in pilot holes which must be provided to accommodate the large profile of the support arm and the cutter. The larger pilot hole requires a larger size bit in the initial drilling operation which is more costly to drill than one using a smaller bit. Finally, changing the cutters on conventional hole openers is time consuming, if it can be accomplished at all, and often requires repair to the opener body and support arms due to damage caused by the pins and locking devices used to secure the cutters to the conventional opener body. Conventional openers typically have welded support arms carrying the cutter and removal of the cutter would entail removing the support arms and re-welding the new support arms after replacing the cutter itself. This extraordinary amount of work generally causes the used or damaged conventional hole opener to be scrapped rather than repaired.